A first objective of this research program is to analyze the solid structure of a well-defined biopolymeric material which can be transformed between two stated: A state in which the biopolymer initiates a vigorous platelet aggregation reaction in vitro and a state in which the biopolymer shows no such activity under identical conditions. The thrombogenic control will comprise collagen fibrils possessing the well-known native banding which is evidence of a solid state with high degree of marcomolecular packing order. The non-thrombogenic material will consist of collagen fibrils which have been precipitated in acidic pH with chondroitin 6-sulfate (and subsequently dialyzed to neutral pH), to give a solid state which, according to recent evidence, has no apparent packing order but one in which the constituent macromolecules maintain the intact triple helical configuration of collagen. Several other types of collagen fibrils, both crystalline and non crystalline will be included in the study. The degree of packing order in the collagen fibrils will be studied by small angle x-ray diffraction and by transmission electron microscopy. The intensity of the collagen-platelet reaction will be studied in vitro by scanning electron microscopy, as well as by platelet aggregometry, demonstration of the secretion of serotonin and Beta-thromboglobulin, demonstration of the generation of theomboxane B2, and measurement of adhesion of platelets. An animal model is also described. A second objective of this study is extension of the results obtained with collagen fibrils to understanding of the thrombogenicity of synthetic polymers.